Killia

Aerodactyl, Honchkrow, Staraptor, Gliscor and Togekiss are all good.

There are three ways, two of which aren't really all that viable for you right now:

1) Choose it as your starter

2) Get at least 300 species of pokemon registered as 'Caught', then speak to an NPC in Agate City. Note that Agate City houses the second-to-last Gym Leader

3) Make use of Reborn's beautiful Online options and trade for it

Sorry, but dem's the breaks at the moment.

should be more than enough to power through stuff

That's good I thought slurpuff would be a burden

Slurpuff and Roserade are definitely what you missed for a flawless type coverage. My last advice would be to teach Belly Drum to Slurpuff by breeding (You'll need a Marill and a Poliwag for this.) That might be tough, but it's by far the best way to turn Slurpuff into a real threat.

Otherwise, I have nothing else to say but good luck  

I'd suggest Roserade as your grass type, also instantly covers Poison

Whoever recommended simple swoobat has my respecc

Klink, Nidoking, Meowstic, Arbok are solid choices for Corey, among others

Cool thanks

My personal top five:

5. Cloyster: Absolutely! The Shell Smash + Icicle Spear combo turns Cloyster into a real threat against a broad range of opponents, don't forget to give it a Power Herb to hold on for long fights. Unfortunately, it's available far too late in the game, only after you get the 13th badge. For obvious reasons, Skill Link is the ability to maximize Cloyster's effectiveness, Overcoat and Shell Armor are not adviced. But still, that won't prevent me to give it a high recommendation!

4. Swampert: Used alongside with a Pokemon knowing the Drizzle ability, it can outspeed everything with a considerable amount of damage. Swampert is by far my second favorite aquatic starter, especially since grass encounters are not very numerous in Reborn after you get the 3rd badge. As a result, Swampert's dual-type won't be that a problem, you can have my word for it! But there's no Swamperite available yet, so you'll have to deal with a normal Swampert until then. Of course, Waterfall has to be part of your moveset if you have one.

3. Milotic: A respectable staller, as well as a good-looking asset to get in your team. Unfortunately, we have the same problem Cloyster has: it's available too late in the game. As a matter of fact, you have to defeat the 12th Gym Leader first to have a chance to find it. Concerning the use of our dear serpentine Pokemon, switching between Mirror Coat and Recover can be a good option to defeat some strong opponents without too much effort, and its defense combined to its health makes that it takes forever to defeat it. By chance, Feebas is not that pain to catch in Reborn, which is quite exceptional compared to the official games. You can give it a try if you want.

2. Mantine: An improved version of Milotic to me. Available before the fight for the 6th badge, I did my first run with a Mantine as my Water Pokemon. I have no regrets. In fact, it's probably one of the best assets to have during the confrontation with the Water Gym Leader. Also, thanks to the Wide Guard move, you'll have a possibility to ignore damage for most of the double battles. Of course, you're free to teach it different moves if you prefer. But since it knows Water Absorb and it's available quite early in Reborn, Mantine outclasses Milotic in my opinion. Also, Aqua Ring + Leftovers is a good combination to make it one of the best stallers of the game, a choice to meditate on.

1. Greninja: The best water Pokemon as well as my favorite starter! Greninja came in handy more than once during most of the hardest fights in the game for me. You can opt between physical offender or special offender, in any case, you can outspeed almost everything without the Drizzle thing or holding a Choice Scarf, let alone the fact that the Protean ability turns it into a pure swiss army knife. And that is the biggest advantage of Greninja: it will learn a huge range of offensive moves of various types without the need of a TM such as Extrasensory or more especially Bounce and Smack Down which can be relatively useful in some specific battlefields. I tend to consider it as a water version of Blaziken. In the end, it's not a coincidence if Ame has chosen to put these two at the end of the available Pokemon list in Reborn. Nevertheless, all the Pokemon being legally catchable in the wild, you don't have to worry if you didn't pick it in the Grand Hall.

Hope that helped

Thanks that helped a lot

You're welcome

Do have any idea of good team

Well, my own early game team was chespin, grubbin, espurr (M), swoobat, magnemite, and growlithe, but magnemite got moved to far later in the game, so... that's a bit of a bummer. Most of these guys have been replaced, though, so I'm not sure how helpful that information will be anyway. ¯\_(ツ)_/¯

it was helpful in a way i guess